This hypothesis is supported by recent data showing HP1 mislocalization, abnormal directly nu clear organization, and developmental arrest in H3. 3 K27R mutant embryos. Modifications of epigenetic marks could also be involved in the reorganization of pericentromeric/centromeric chro matin. Complex and asymmetric histone/DNA modifica tions occur continuously Inhibitors,Modulators,Libraries throughout early development in both parental genomes and may regulate the balance between pericentromeric elongated versus compact structures. Finally, regarding other factors that might play a role in heterochromatin assembly and organization, it must be recalled that an unidentified RNA is an integral com ponent of pericentromeric heterochromatin in humans and is necessary for the accumulation of HP1 on pericentromeric heterochromatin.

Moreover, small centromeric RNAs are involved in murine centromeric heterochromatin assembly, and in mouse embryos, small RNAs seem to participate in the formation of chromocenters as shown by the use of locked nucleic acid DNA gapmers to interfere with the tran scription of major satellites in early embryos. This induces developmental arrest before the completion of chromocenter formation. Inhibitors,Modulators,Libraries Conclusions Altogether, our results show that significant genome re structuring occurs during the entire preimplantation period. Just after fertilization, Inhibitors,Modulators,Libraries zygotes have a very peculiar nuclear organization with highly decondensed pericentro meric heterochromatin structures. During the next cell cycle, nucleolar precursor bodies and pericentromeric heterochromatin undergo important reorganization, as previously described in the literature.

However, thanks to new computational tools, we were able to analyze these elements for the first time in a large number of embryos, all the way up to the blasto cyst stage. We believe that these tools could now be used to enable detailed analyses of fluorescent 3D images in other models/organisms. Specifically, Inhibitors,Modulators,Libraries we consider compu tational imaging Inhibitors,Modulators,Libraries a promising approach to explore large scale nuclear movements. We also demonstrated that the 4 cell stage represents a major step in preimplantation development, especially with regards to pericentromeric structures. Pericentro meric structures may impact the regulation of develop mental genes, particularly on heterochromatin dependent gene silencing.

As in somatic cells, the role of these rear rangements during preimplantation development may be to bring different nuclear compartments in close proximity in order to activate/ repress specific genes yet to be identified. Methods Ethics statement Animal care and handling were carried out according Ceritinib cancer to European regulations on animal welfare. NB has the authorization to work with laboratory animals from the departmental veterinary regulatory service and from the local ethics committee.